Repeater circuits



Aug. 14, 1928. 1,680,367

c. s. DEMAREST REPEATER CIRCUITS Filed -July 1922 Low r2550,"- gas ascpnielzi- INVEN TOR.

& ATTORNEY Patented Aug. 14, 1928.

UNITED STATES PATENT OFFICE.

CHARLES S. DEMAREST, OF RIDGEWOQD, NEW JERSEY, ASSIGNOR TO AMERICANTELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

REPEATER CIRCUITS.

Application filed July 7,

This invention relates to improvements in repeater circuits and moreparticularly to circuits employing as the repeater element an ionizedgas tube. The invention is applicable, among other uses, to telephonyfor the purpose of obtaining in an'outgoing circuit an amplification ofvoice currents originating in an incoming circuit. It is also applicableto tclegraphy and signaling'systems in general, where amplification isnecessary in receiving, recording or reproducing impulses of electricalenergy.

Certain types of telephone repeaters now in-use employ as the repeaterelement a vacuum tube with a heated electrode as a source of freeelectrons. It has been found in practice that considerable energy isrequired to keep this electrode at the desired temperature, particularlyin large telephone repeater installations. In such cases the vacuum tubefilament current often amounts to several hundred amperes from a 21-voltbattery.- Furthermore, the life of this type of vacuum tube is largelydetermined by that of the heated filament. A practical method ofeliminating the heated electrode in amplifiers utilized in telephonerepeater circuits would, accordingly, be of considerable economic valueand is one of the primary objects of the arrangements of this invention.

The repeater element of the invention comprises a tube which depends onthe presence of ionized gas for its operation. In the tube is a gas,such for example as neon, at low ressure, which has the property ofdecreas- :mg in electrical resistance as the potential across theterminals of the tube is increased. Any suitable gas, other than neon,which has such properties might be utilized in this connection. The tubewill have four electrodes or terminals. The gas in the tube will beplaced in a state of ionization and form a conducting path between thetwo electrodes connected to the outgoing circuit. The variation ofotential across the two electrodes connects to the incoming circuitcaused by the fluctuating voice, or signal waves, will vary theresistance of the gas and cause similar fluctuations of the current inthe outgoing circuit. Other features and objects of the invention willappear more fully from the detailed description hereinafter given.

The invention may be morefully undershown, to give a constant potentialacross electrodcs3 and 4. This places the gaseous content of the tube inthe proper state of ionization to be uniform in its action and sensitiveto the varying potential received from the line section L The varyingpotential due to the fluctuations of the voice waves thus applied causesa. change in ionization in the gas. The resistance between electrodes 8and 9 will vary inversely with the degree ofionization. The electrodes 8and 9 are connected through a resistance 10, battery 11, and transformer2, to the output section L of the transmission line. The

change in resistance in the path through the tube between electrodes 8and 9 causes fluctuations in the current flow in the output circuit dueto the local battery 11 and these fluctuations are proportional to theincoming lineeurrents which are desired to be amplified. The amplitudeof,the current fluctuations may be greater in the output clrcuit than inthe input circuit due to the energy supplied by the local battery 11.The resistances 5 and 10 are provided to limit the current in the tubeand give stability of operation. The retard coil 6 is provided 1n orderthat the potential of the electrodes 3 and 4 will vary in accordancewith the incoming line currents. .It is desirable that the innerelectrodes 3 and 4 be of some form, such as a grid, that will permit thepassage of ions between the two outer electrodes 8 and 9. With thisarrangement amplification of the incoming currents maybe secured and theuse of a heated electrode in the tube may be obviated.

While the arrangements of the invention have been showiras illustratedin certain specific arrangements which are deemed desirable, it isunderstood that they are capable of embodiment in many and widely variedforms without departin from the spirit of the invention as defined bythe appended claims.

What is claimed is:

1-.A repeater system comprising .a tube having a gaseous'content thestate of ionization of which will var in direct proportion to thepotential to which it is subjected, a pair ofelectrodes in said tubebetween which is applied a potential varying in accordance with signalcurrents coming in over said system, and a second pair of electrodesconnected to an output circuit of said system, the current in saidoutput circuit varying in accordance with the incoming signal currents,said first mentioned pair of electrodes being positioned between saidsecond mentioned pair of electrodes and being independent of anyconnection therewith.

2. A repeater system comprising a tube having two sets of electrodes, aninput circuit on which are impressed potential variations due to signalcurrents, said input circuit terminating at one of said sets ofelectrodes, and an output circuit connected to said other set ofelectrodes, said tubes having a gaseous content through which a stableglow discharge is maintained between said output circuit electrodessubstantially free from any thermionic emission from any of saidelectrodes, the currents in said glow discharge bein varied by thepotentials impressed on sai electrodes in said input circuitindependently from the potentials applied to said other electrodes.

3. A repeater system comprising a tube having two sets of electrodesconnected independently from each other, an input circuit on which areimpressed potential variations due to signal currents, said inputcircuit terminating at one of said sets of electrodes, a resistance andan inductance and a constant source of potential bridged across saidinput circuit, an output circuit connected to said other set ofelectrodes, said tube having a gaseous content maintained in a state ofionization due to said stabilizing resistance and said last mentionedsource of current resulting in a steady luminous discharge between saidlast mentioned set of electrodes.

4. A tube having a low pressure content of gas of the helium group, apair of electrodes, an output circuit connected to said electrodes andincluding a resistance and a source of current, said resistance andsource of current being so adjusted that the potential gradient betweensaid electrodes will be that characteristic of a glow discharge, asecond pair of electrodes included in said tube positioned between saidfirst mentioned pair of electrodes and independent of any connectiontherewith, and means to apply potentials thereto whereby said potentialgradient may be varied.

In testimony whereof, I have signed my name to this specification this5th day of July, 1922.

CHARLES S. DEMAREST.

